"The Death Cure" is a potent grand finale to a science-fiction trilogy of occasionally murky intentions. As the concluding chapter adapted from James Dashner's dystopian YA book seriesfollowing 2014's solidly engaging, labyrinth-set "The Maze Runner" and 2015's more routine, sandswept "The Scorch Trials"the scope feels larger, the stunts grander, the story more urgent. For a triptych of films that has predominately kept its characters in the dark about their own pasts, returning director Wes Ball and scribe T.S. Nowlin at last delve beneath the surface of who they areeven if, it should be noted, there is still precious little information offered about where they come from. There is a certain symmetry in taking time to focus on personal interiors, these appreciable dramatic beats running parallel to a plot that finds our hero Thomas (Dylan O'Brien) and his friends Newt (Thomas Brodie-Sangster), Frypan (Dexter Darden) and Brenda (Rosa Salazar) endeavoring to breach the walls of a supposed safe-haven metropolis built to keep out the deadly virus that has decimated most of the world's population.

Minho (Ki Hong Lee) has been captured by WCKD. Having regained her memories, conflicted former ally Teresa (Kaya Scodelario) has turned her back on her comrades and declared her allegiance to the nefarious organization's murderous search for a cure. With more lives at stake and the virus threatening to become airborne, WCKD head Ava Paige (Patricia Clarkson) has begun to lose hope while assistant director Janson (Aidan Gillen) grows increasingly desperate to find a test subject whose blood holds the key to an antibody. What begins as an undercover mission to save Minho becomes something altogether more fateful for Thomas and his pals, their operation and that of the ethically clouded WCKD coming to a head as the epidemic closes in.

With showmanship to spare, "The Death Cure" provides a taut, satisfying, oft-gripping 142-minute climax to an apocalyptic tale that stumbled a bit while spinning its wheels during middle chapter "The Scorch Trials." Jumping immediately into the action with a daring hijacking of a locomotive car carrying WCKD's latest young abductees (it helps immensely, by the way, to refresh oneself on the previous films prior to seeing this one), the picture means business while edging closer to a resolution. Perilous, craftily conceived set-pieces are thrown quickly and furiously at the viewer, each one impressive in its grandeur and ambition (a sequence where a bus of passengers is lifted above the nighttime city by construction equipment ill-equipped to handle so much weight is awesome to behold). All the while, director Wes Ball continues to raise the stakes while never losing sight of the interpersonal drama of its brave, put-upon protagonists and their less savory adversaries. From this, a provocative question of right-or-wrong morality is explored: if the possibility for a cure still exists, is it okay to sacrifice the lives of an innocent few in order to potentially save the rest of the surviving population? Ball and screenwriter Nowlin smartly do not provide an answer, but there is no secret where its characters side on this debate.

Dylan O'Brien (2016's "Deepwater Horizon"), whose serious on-set injuries during the first week of principal photography led to a shooting delay of nearly a year, has always been quite charismatic in the lead role of Thomas, but here he graduates into a fully grown-up performer with a clearly promising career ahead of him. O'Brien is a plausible, enthralling, strong yet vulnerable hero who carries the proceedings. Matching him beat for beat is Kaya Scodelario (2017's "Pirates of the Caribbean: Dead Men Tell No Tales") as Teresa, struggling to overcome guilt for selling her friends out in exchange for what she has told herself is a greater good. Scodelario, who felt perhaps a little bland at the start of the series, is now anything but; her Teresa has arguably the most sizable arc and dimension of all the central players, guided by the emotional connection she shares with Thomas even when they are physically separated. As WCKD head Ava Paige, the terrific Patricia Clarkson (2011's "One Day") has thankfully received more complex facets to explore; for the first time, she isn't seen as a one-note heavy, but someone who is facing her own mortality and beginning to question the grisly work her extremist organization has been doing. "If we find a cure," Ava tells Janson as she gazes down on a twinkling city in grave danger, "that's the only way this was worth it."

One of the attributes of "The Maze Runner" and its follow-ups has been their diversity; despite weaving a single ongoing story, each one has been respectively different from the last in their locale and genre. "The Maze Runner" was a fantasy-laden monster movie with a "Lord of the Flies" bent. "The Scorch Trials" was a desert-set zombie flick in the mold of "The Walking Dead." "The Death Cure" includes elements of both its predecessors while feeling like a sci-fi-tinged "Die Hard," only more extravagant in scale. Still, taken on a film-by-film basis, they haven't matched the lofty heights of their watermark brethren. In the grand scheme of YA page-to-screen sagas, the material hasn't the depth or resonance of "Harry Potter" or the ripe social commentary of "The Hunger Games." The maze setting gave the first film a unique calling card, but once the protagonists escaped, the series threatened to become little more than a variation on the ill-fated "Divergent" franchise (which, outrageously, saw its concluding installment canceled when Lionsgate greedily separated the finale into two parts and the first one, 2016's "Allegiant," underperformed at the box office). All comes full circle with "The Death Cure," which has fortunately not only finished the story begun in 2014, but wrapped it up in just about as strong a manner as one could imagine. Running nearly two-and-a-half hours but never striking as excessive or bloated, the film works like gangbusters clear through to its quietly ruminative final moments, a tribute to everything lost and that which is ultimately gained for its survivors. Filmmakers of like-minded future franchises, take note: this is how you take a heretofore middle-of-the-road trilogy and give it the consequence and breadth necessary to individually and cumulatively transcend all expectations.